Observation of the 87 Rb 5S 1/2 to 4D 3/2 electric quadrupole transition at 516.6 nm mediated via an optical nanofibre

Light guided by an optical nanofibre has a very steep evanescent field gradient extending from the fibre surface. This gradient can be exploited to drive electric quadrupole transitions in nearby quantum emitters. In this paper, we report on the observation of the 5S 1/2 → 4D 3/2 electric quadrupole transition at 516.6 nm (in vacuum) in laser-cooled 87 Rb atoms using only a few μ W of laser power propagating through an optical nanofibre embedded in the atom cloud. This work extends the range of applications for optical nanofibres in atomic physics to include more fundamental tests such as high-precision measurements of parity non-conservation.